1. Field of the Invention
The present invention relates generally to methods and systems for the detection of chemical agents. More particularly, the present invention relates to the use of multiple types of chemical agent detectors having overlapping performance.
2. Description of Related Art
Sensors capable of detecting the presence of chemical agents and quantifying the amount of agent present are known. These sensors can be grouped into at least two types, e.g., analytical and phenomenological. Typically, an analytical sensor, such as a mass spectrometer, directly measures some characteristic of the environment, e.g., the mass and relative concenration of atoms or molecules. While capable of high accuracy and low false alarm rate, analytical sensors are typically expensive, cumbersome, and slow—requiring significant preparation and calibration activity.
Phenomenological sensors can be characterized as detecting an event which points to the presence of a chemical agent; e.g., a change in the resistance of a semiconductor that has been coated with a substance responsive to one or more specific chemical agents. Typical phenomenological sensors consist of an array of elements that can be trained to recognize patterns of phenomena. Existing sensors that can be characterized as phenomenological include Ion Mobility (IM) cells, chemo-resistive sensors, metal-oxide sensors, and Surface Acoustic Wave (SAW) devices. Some sensors of these types are capable of detecting several types of chemical agents, are relatively small (especially in comparison to analytical sensors), and potentially inexpensive in large quantities. However, these sensors have not displayed a false alarm rate required by many applications.
While sensor systems exist that combine more than one detection technology, the sensors in such existing systems have distinct, non-overlapping, capabilities. For example, the Hazmat CAD (Chemical Agent Detector) from Microsensor Systems, Inc. of Bowling Green Kentucky uses both a SAW and an electrochemical sensor. The two sensors have distinct capabilities. The electrochemical sensor only provides detection of hydrogen cyanide (HCN); it does not provide detection capability overlapping with the SAW.
Typical multi-sensor systems have not satisfactorily addressed issues related to airflow in devices comprising more than one sensor type—especially where different sensor types have different cycle times and flow requirements. Further, typical sensor systems are susceptible to contamination, aspiration of water, adsorption of volatiles that may later be out-gassed, and the uptake of potentially abrasive solid particles such as dirt, dust, or sand.